Temperature indicator

ABSTRACT

A temperature indicator including a backing strip with an embossed well stamped therein is provided. The well contains a matrix carrier which is impregnated with a thermally responsive fusible chemical. The bottom of the well is painted a bright color. The impregnated matrix is placed over and substantially covers the colored bottom of the well. The top of the well is covered by a transparent film. At a temperature below a predetermined level, the colored bottom of the well is substantially invisible due to the impregnated matrix being opaque, and at temperatures above such predetermined level, the colored bottom of the well is clearly visible due to the transparency of the impregnated matrix upon melting of the chemical.

BACKGROUND OF THE INVENTION

This invention relates to temperature indicators. More particularly, itrelates to high temperature reversible indicators having a dot whichchanges from an opaque to a transparent mode as a means for indication.It is particularly useful in monitoring leaky steam traps.

Temperature indicators which utilize chemicals changing from an opaqueto a transparent mode as they pass from a solid to a liquid phase, havebeen used in the past particularly in the human clinical thermometerindustry. One example of this phenomena is set forth in U.S. Pat. No.3,859,856, issued to Kay Laboratories. The Kay Laboratory patent shows ahuman clinical thermometer which has a colored backing with a pluralityof chemicals disposed thereon at discreet locations. The chemicalsdisplay the characteristic of changing from opaque to transparent uponreaching certain predetermined temperatures corresponding to those inthe human clinical range. Thus the colored backing is invisible belowpredetermined temperatures and becomes visible above such temperaturesas the chemicals melt.

Another example of this phenomena is disclosed in U.S. Pat. No.1,676,536 issued to Carl A. Ferkel. The Ferkel patent discloses atemperature indicating device having 3 compartments which housematerials changing from opaque to clear at predetermined temperatures.At the bottom of the compartments are printed the words Warm, Hot andDanger indicating various levels of temperature. The Ferkel device isadapted to be attached to a pipe which may be used in a distillationprocess.

U.S. Pat. No. 3,580,079 issued to Abbott Laboratories discloses adisposable clinical thermometer including a plurality of windows whichare made translucent by roughing its inner surfaces to diffuse light asit passes therethrough. A chemical is provided in cells which arecovered by the roughened windows which melts at a predeterminedtemperature. When the chemicals melt, it comes into contact with thewindow optically smoothing the window and permitting the bottom of thecell to become visible. Temperature numbers are printed at the bottom ofeach cell.

U.S. Pat. No. 3,065,083 issued to Albert Gessler discloses a time-delaytemperature indicator which includes a grid which is used to prevent thespread of molten materials when the device is activated.

Of particular interest herein is the use of such an indicator to monitorsteam traps. The rapidly increasing costs of producing steam hasresulted in a renewed interest in efficient steam trapping and bettersteam trap maintenance. In general, steam traps are devices whichcollect condensation or water from the steam lines and recirculate thewater back to a boiler. Normally, a steam trap is activated when anamount of water accumulates in the trap causing a valve to open for avery short period of time thus permitting the water which hasaccumulated therein to flow into the return line. A minor amount ofsteam often escapes the steam line when this valve is open. Problemsarise, however, when the valve becomes stuck open. This permits thesteam to flow from the steam line into the return water line, resultingin the loss of a great deal of steam. It has been calculated that on1978 costs for producing steam at 100 psi that a 1/2 inch leaking lineresults in a $30,000 per year loss.

In order to eliminate or reduce losses of this type, steam traps must beroutinely checked for leaks. Many expensive and time-consumingtechniques of monitoring steam traps have been used. Some of theseinclude pressure gauges on steam supply systems and condensate receivertanks; listening devices such as an industrial stethoscope on the steamtrap and portable contact pyrometers for measuring temperatures on bothsides of the traps.

Recently, devices have come onto the market which contain a small dotthat responds to certain temperatures by changing colors. One example ofsuch a device is the so-called Steam Trap Watchdog manufactured and soldby Reliance Brooks, Inc. This device is a small 1"×4" strip whichcontains a small dot responding to a specific temperature by changingcolor. Although the application of the Watchdog device is simple andinexpensive, still this device has a number of deficiencies. Forexample, the color change of the device is irreversible, the differentcolors of the indicating dot are not easily discernable from a distanceof several feet and as many as 11 different devices are needed tomonitor steam line pressures ranging from 40 to 300 psi. In addition tothese deficiencies, there are several common steam trapping situationsin which a properly functioning steam trap could activate this device.Furthermore, since this device is irreversible the devices must bereplaced any time after they are fired. Also, they might easily give afalse indication that there is a problem with the steam trap since oncethey are exposed to the temperatures at which they fire, they continueto indicate that there is a problem. Thus, there is a need for areversible steam trap monitoring device.

One of the major problems in the use of reversible opaque to transparentthermometers and temperature indicators which have been previouslydescribed above, particularly in steam trap monitor applications, isthat unless the devices remain horizontal, the chemicals will run to thesides of their holding pocket thus showing a portion of the bottom ofthe pocket of one color and another portion being opaque. This is aparticular problem in the steam trap monitor application where thedevice might be wrapped around a pipe in a vertical position, so that itis easily read. Of course, absorbent layers could be used as shown inthe General Dynamics U.S. Pat. No. 3,059,474; however, this would renderthe device an irreversible device with all the drawbacks describedabove. It is, therefore, desirable to provide an improved temperaturemonitor which takes advantage of the opaque to transparent mode ofoperation without the accompanying drawbacks.

OBJECT OF THE INVENTION

It is one object of this invention to provide an improved temperatureindicator.

It is another object of this invention to provide a reversibletemperature indicator which is inexpensive and easily readable.

It is another object of this invention to provide a reversibletemperature indicator which is simple in construction.

It is still another object of this invention to provide an improvedreversible steam trap monitor.

SUMMARY OF THE INVENTION

In accordance with one form of this invention, there is provided atemperature indicator having a substrate with an embossed well therein.A substantially transparent cover is provided over the well. The bottomof the well is of a readily discernable color. A carrier is received inthe well and is impregnated with a chemical. The chemical is solid belowa predetermined temperature and liquid above the predeterminedtemperature. A substantial amount of the chemical remains in the carrierin both the liquid and solid phases. The color of the bottom of the wellis visible when the chemical is in its liquid phase and substantiallyinvisible when it is in its solid phase.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter which is regarded as the invention is set forth inthe appended claims. The invention itself, however, together withfurther objects and advantages thereof, may be better understood byreference to the following description taken in conjunction with theaccompanying drawings in which:

FIG. 1 is a top plan view of the device showing one embodiment of thesubject invention where the indicator dot is in its opaque state;

FIG. 2 shows the device of FIG. 1 in which the indicator dot is in itstransparent state;

FIG. 3 is a cross-sectional side view of the indicator of FIG. 1;

FIG. 4 shows the matrix carrier as partially shown in FIG. 3;

FIG. 5 is an end elevational view of the indicator of FIG. 1;

FIG. 6 shows an example of an indicator which does not use a carriermatrix and is not a part of this invention.

FIG. 7 shows an alternative carrier to the one shown in FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now more particularly to FIG. 1, there is provided temperatureindicator 10 which is particularly adapted to monitor steam traps. Theindicator includes indicator chemical 12 which as shown in FIG. 1, is inits opaque stage. The device shown in FIG. 2 shows the indicator dot 12in its transparent stage, thus showing the bottom of embossed well 14 asshown in FIG. 3. Well 14 may be punched in a thin strip 16 of aluminumor Teflon FEP. The bottom inside of the well 14 is painted a brightcolor as shown as color layer 18. The thin strip is covered by aoptically clear film 20 which may be FEP or a polyimide tape. This tapeis transparent so that one may view the inside of the well. If the film20 and strip 16 are both FEP, then they are readily heat sealed to eachother. If an aluminum/polymide system is used, then normally a siliconeadhesive will be used to seal the two together.

The device includes a carrier 24 which lays across and substantiallycovers the colored bottom of the embossment. Carrier matrix 24 isimpregnated with a chemical which changes phase such that is goes fromthe solid phase to the liquid phase at and above a predeterminedtemperature. The carrier, which is disc shaped, may be made of amaterial such that light will be refracted and thus maintain an opaquecover over the painted bottom of the indicator. This opacity may befurther enhanced by the fact that the chemical 12 impregnated thereinmay also be opaque in its solid state, and, furthermore, may be of adifferent index of refraction than the disc carrier 24 such that thelight entering into the well will be refracted at different angles goingthrough the boundaries between the carrier and the chemical 12. Thepreferred disc, shown in FIG. 4, is a Teflon TFE disc made from a meshsheet of TFE fibers called Specta-Mesh, available from Spectrum MedicalIndustries, Inc. Another type of disc which has been used is a WhatmanGlass Filter Paper, shown in FIG. 7 and available from the WhatmanCompany. Other types of discs, such as those made of nonwoven polyester,again exemplified in FIG. 7, have also been used.

The chemical which changes phase at a predetermined temperature, in thepreferred embodiment, changes in the range of approximately 40° C. to200° C. which will provide an indication that steam is passing throughthe steam trap for various steam pressures. One such class of chemicals12 are alkane hydrocarbons indicated by the general formula C_(n)H_(2n+2). The preferred hydrocarbons are waxes which are moderated bystable chemicals with sharp melting points. One such wax is Verba-8 wax,available from Dura Commodities Corp. Other types of chemicals 12 whichmay be used are waxes which are particularly opaque in their solidphase. In order for the color to be very clearly visible, it is bestthat the liquid phase of the chemical 12 have an index of refractionsubstantially the same as that of the carrier. Furthermore, the matrix24 is of such a pore size that it will hold the impregnated chemical 12in place during both the solid and the liquid phases. That is importantfor such uses as steam trap monitors where the indicator dot 12 may bein a vertical position. Since the device is reversible, once thechemical 12 has melted, without a carrier matrix 24, it would tend tofall to the sides of the well during the liquid phase and thenresolidify in that position leaving a half transparent and half opaqueindicator. An example of an indicator which uses an opaque totransparent chemical but not a carrier matrix is shown in FIG. 6. This,of course, could be a source of confusion to the observer. Thus, certaintypes of porous matrices 24 provide the dual function of holding thethermally responsive chemical 12 in place in both the solid and liquidphase, and provides an opacity while the chemical is in its solid phasedue to the refraction of light around the fibers or pores within thematrix 24 which may be further enhanced by the opacity of the chemical12 selected in its solid phase.

Furthermore, in certain embodiments, the matrix will permit a clearlyvisible view of the colored bottom of the well when the chemical meltsdue to the fact that the liquid chemicals have substantially the sameindex of refraction as the matrix. Below are some examples whichincorporate features of the invention.

EXAMPLE I

A small disc cut from Teflon TFE was impregnated with 0.062 grams ofVerba-8 wax and then placed in a Teflon FEP well that had a red-coloredbottom. The disc was covered with another strip of FEP and the twostrips of FEP were heat sealed together. This device was attached in avertical position to the outside surface of a steam pipe. Thetemperature of the pipe was slowly increased and the wax melted to atransparent liquid as steam entered the pipe. This liquid caused the TFEdisc to become transparent and the red color became visible. Thetemperature of the pipe was allowed to decrease and the wax wassolidified and blocked the red color from view.

EXAMPLE II

A small disc cut from Whatman Glass Filter Paper was treated with 0.028grams of α,α-dichloro-p-xylene and then placed in an aluminum well thathad a red-colored bottom. The disc was covered with a piece of 3Mpolyimide tape and the pan was then heat sealed to another piece of thesame coated aluminum which contained a hole that was slightly smallerthan the disc. This device was attached in a vertical position to theoutside surface of the steam pipe. The temperature of the pipe wasslowly increased and between the temperatures of 105° and 110° C. theα,α-dichloro-p-xylene melted to a transparent liquid. This liquid causedthe glass filter paper to become transparent and a red color becamevisible through the window. The temperature of the pipe was allowed todecrease, and the α,α-dichloro-p-xylene solidified and a white solid wasvisible to block the red color from view.

The indicator includes a layer of adhesive 26 which is attached to thebottom of the device so that it may be readily attached to a pipe in asteam trap. One adhesive which has been used is Densil 2078, availablefrom Dennison Company.

From the foregoing description of the embodiments of the invention, itwill be apparent that many modifications may be made therein. It will beunderstood, however, that these embodiments of the invention areintended as exemplifications of the invention only and that theinvention is not limited thereto. It will be understood, therefore, thatit is intended in the appended claims to cover all modifications as fallwithin the true spirit and scope of the invention.

I claim:
 1. A reversible steam trap temperature indicator,comprising:(a) a substrate having an embossed well therein; (b) asubstantially transparent cover over said well, the bottom of said wellbeing a detectable color; (c) a porous or fibrous carrier received insaid well, said carrier voids impregnated with a chemical which is solidbelow a predetermined temperature and liquid above said predeterminedtemperature, said carrier adapted to refract light to maintain an opaquecover over the painted bottom of said indicator at least when saidchemical is solid; (d) a substantial amount of said chemical remainingin said carrier in both liquid and solid phases, and the color of thebottom of said well being visible when said chemical is in its liquidphase and substantially invisible when it is in its solid phase.
 2. Thedevice as set forth in claim 1 wherein the chemical is a hydrocarbon. 3.The device as set forth in claim 1 wherein said chemical changes fromopaque to transparent at said predetermined temperature.
 4. The deviceas set forth in claim 1, wherein the combination of the carrier and thechemical caused the visibility and invisibility of said colored bottom.5. The device as set forth in claim 1 wherein said carrier is opticallyopaque when said chemical is solid and optically smooth and thustransparent when said chemical is liquid.
 6. The indicator set forth inclaim 2 wherein said hydrocarbon is of the general formula C_(n)H_(2n+2).
 7. The device as set forth in claim 1 wherein said chemical isα,α-dichloro-p-xylene.
 8. The indicator as set forth in claim 1, whereinsaid carrier contains pores of such dimension so as to hold saidchemical therein during its liquid phase.
 9. A temperature indicator,comprising:(a) a substrate having an embossed well therein; (b) asubstantially transparent cover over said well, the bottom of said wellbeing a detectable color; (c) a carrier received in said well, saidcarrier impregnated with a chemical which is solid below a predeterminedtemperature and liquid above said predetermined temperature, whereinsaid carrier is a matrix containing pores of such dimension so as tohold said chemical therein during its liquid phase, and wherein saidcarrier matrix is a TFE disc; and (d) a substantial amount of saidchemical remaining in said carrier in both liquid and solid phases, andthe color of the bottom of said well being visible when said chemical isin its liquid phase and substantially invisible when in its solid phase.10. The device as set forth in claim 1, wherein said carrier is a glassfilter paper.
 11. The device as set forth in claim 1, wherein saidcarrier is non-woven polyester.
 12. The device as set forth in claim 1,wherein the indicator is a steam trap monitor.